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href="/frontend/javascript/error.html" class="sidebar-link">Error 类型</a></li><li><a href="/frontend/javascript/function-methods.html" class="sidebar-link">对象的构造函数方法</a></li><li><a href="/frontend/javascript/implicit-coercion.html" class="sidebar-link">隐式转换</a></li><li><a href="/frontend/javascript/invocation-expression.html" class="sidebar-link">调用表达式</a></li><li><a href="/frontend/javascript/invoking-functions.html" class="sidebar-link">函数调用</a></li><li><a href="/frontend/javascript/prototype-chain.html" class="sidebar-link">原型链</a></li><li><a href="/frontend/javascript/resolve-function-call-in-jsx.html" class="sidebar-link">处理 JSX 中函数调用</a></li><li><a href="/frontend/javascript/scope-and-closures.html" class="sidebar-link">作用域与闭包</a></li><li><a href="/frontend/javascript/statements-and-expressions.html" class="sidebar-link">语句和表达式</a></li><li><a href="/frontend/javascript/this-identifier.html" class="sidebar-link">this 关键字</a></li></ul></section></li><li><section class="sidebar-group depth-0"><p class="sidebar-heading"><span>对象方法</span> <!----></p> <ul class="sidebar-links sidebar-group-items"><li><a href="/frontend/javascript/object-constructor-methods.html" class="sidebar-link">对象的构造函数方法</a></li><li><a href="/frontend/javascript/object-constructor-methods-freeze.html" class="sidebar-link">对象构造函数冻结方法</a></li><li><a href="/frontend/javascript/object-constructor-methods-property.html" class="sidebar-link">对象构造函数属性方法</a></li><li><a href="/frontend/javascript/object-instance-methods.html" class="sidebar-link">对象的实例函数方法</a></li></ul></section></li><li><section class="sidebar-group depth-0"><p class="sidebar-heading open"><span>数组方法</span> <!----></p> <ul class="sidebar-links sidebar-group-items"><li><a href="/frontend/javascript/array.html" class="sidebar-link">数组</a></li><li><a href="/frontend/javascript/array-accessor-methods.html" class="active sidebar-link">数组的访问方法</a><ul class="sidebar-sub-headers"><li class="sidebar-sub-header"><a href="/frontend/javascript/array-accessor-methods.html#array-prototype-concat" class="sidebar-link">Array.prototype.concat</a></li><li class="sidebar-sub-header"><a href="/frontend/javascript/array-accessor-methods.html#array-prototype-includes" class="sidebar-link">Array.prototype.includes</a></li><li class="sidebar-sub-header"><a href="/frontend/javascript/array-accessor-methods.html#array-prototype-indexof" class="sidebar-link">Array.prototype.indexOf</a></li><li class="sidebar-sub-header"><a href="/frontend/javascript/array-accessor-methods.html#array-prototype-join" class="sidebar-link">Array.prototype.join</a></li><li class="sidebar-sub-header"><a href="/frontend/javascript/array-accessor-methods.html#array-prototype-lastindexof" class="sidebar-link">Array.prototype.lastIndexOf</a></li><li class="sidebar-sub-header"><a href="/frontend/javascript/array-accessor-methods.html#array-prototype-slice" class="sidebar-link">Array.prototype.slice</a></li><li class="sidebar-sub-header"><a href="/frontend/javascript/array-accessor-methods.html#array-prototype-tostring" class="sidebar-link">Array.prototype.toString</a></li><li class="sidebar-sub-header"><a href="/frontend/javascript/array-accessor-methods.html#array-prototype-tolocalestring" class="sidebar-link">Array.prototype.toLocaleString</a></li></ul></li><li><a href="/frontend/javascript/array-iteration-methods.html" class="sidebar-link">数组的迭代方法</a></li><li><a href="/frontend/javascript/array-mutator-methods.html" class="sidebar-link">数组的修改方法</a></li></ul></section></li><li><section class="sidebar-group depth-0"><p class="sidebar-heading"><span>字符串方法</span> <!----></p> <ul class="sidebar-links sidebar-group-items"><li><a href="/frontend/javascript/string-concat.html" class="sidebar-link">字符串拼接方法</a></li><li><a href="/frontend/javascript/string-format.html" class="sidebar-link">字符串格式化方法</a></li><li><a href="/frontend/javascript/string-query.html" class="sidebar-link">字符串查询方法</a></li><li><a href="/frontend/javascript/string-regexp.html" class="sidebar-link">字符串正则方法</a></li><li><a href="/frontend/javascript/string-substring.html" class="sidebar-link">字符串截取方法</a></li></ul></section></li></ul> </aside> <main class="page"> <div class="theme-default-content content__default"><h2 id="array-prototype-concat"><a href="#array-prototype-concat" class="header-anchor">#</a> Array.prototype.concat</h2> <h3 id="_1-语法"><a href="#_1-语法" class="header-anchor">#</a> 1. 语法</h3> <div class="custom-block danger"><p class="custom-block-title">WARNING</p> <p>arr.concat(value1[, value2[, ...[, valueN]]])</p></div> <p>参数：</p> <ul><li>valueN：数组或值。</li></ul> <p>返回值：</p> <p>一个新的数组实例。</p> <h3 id="_2-描述"><a href="#_2-描述" class="header-anchor">#</a> 2. 描述</h3> <p><code>concat</code> 方法创建一个新的数组，它由被调用的对象中的元素组成，每个参数的顺序依次是该参数的元素（如果参数是数组）或参数本身（如果参数不是数组）。它不会低轨道嵌套数组参数中。</p> <p><code>concat</code> 方法不会改变 this 或任何作为参数提供的数组，而是返回一个浅拷贝，它包含与原始数组相结合的相同元素的副本。</p> <blockquote><p>个人在日常开发中常用场景：</p> <ul><li>偶尔需要拼接数组时会使用。</li></ul></blockquote> <h3 id="_3-示例"><a href="#_3-示例" class="header-anchor">#</a> 3. 示例</h3> <ul><li><p>concatenating two arrays</p> <div class="language-js extra-class"><pre class="language-js"><code><span class="token keyword">const</span> letters <span class="token operator">=</span> <span class="token punctuation">[</span><span class="token string">'a'</span><span class="token punctuation">,</span> <span class="token string">'b'</span><span class="token punctuation">,</span> <span class="token string">'c'</span><span class="token punctuation">]</span><span class="token punctuation">;</span>
<span class="token keyword">const</span> numbers <span class="token operator">=</span> <span class="token punctuation">[</span><span class="token number">1</span><span class="token punctuation">,</span> <span class="token number">2</span><span class="token punctuation">,</span> <span class="token number">3</span><span class="token punctuation">]</span><span class="token punctuation">;</span>
letters<span class="token punctuation">.</span><span class="token function">concat</span><span class="token punctuation">(</span>numbers<span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// ['a', 'b', 'c', 1, 2, 3]</span>
</code></pre></div></li> <li><p>concatenating three arrays</p> <div class="language-js extra-class"><pre class="language-js"><code><span class="token keyword">const</span> num1 <span class="token operator">=</span> <span class="token punctuation">[</span><span class="token number">1</span><span class="token punctuation">,</span> <span class="token number">2</span><span class="token punctuation">,</span> <span class="token number">3</span><span class="token punctuation">]</span><span class="token punctuation">;</span>
<span class="token keyword">const</span> num2 <span class="token operator">=</span> <span class="token punctuation">[</span><span class="token number">4</span><span class="token punctuation">,</span> <span class="token number">5</span><span class="token punctuation">,</span> <span class="token number">6</span><span class="token punctuation">]</span><span class="token punctuation">;</span>
<span class="token keyword">const</span> num3 <span class="token operator">=</span> <span class="token punctuation">[</span><span class="token number">7</span><span class="token punctuation">,</span> <span class="token number">8</span><span class="token punctuation">,</span> <span class="token number">9</span><span class="token punctuation">]</span><span class="token punctuation">;</span>

num1<span class="token punctuation">.</span><span class="token function">concat</span><span class="token punctuation">(</span>num2<span class="token punctuation">,</span> num3<span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// [1, 2, 3, 4, 5, 6, 7, 8, 9]</span>
</code></pre></div></li> <li><p>concatenating values to an array</p> <div class="language-js extra-class"><pre class="language-js"><code><span class="token keyword">const</span> letters <span class="token operator">=</span> <span class="token punctuation">[</span><span class="token string">'a'</span><span class="token punctuation">,</span> <span class="token string">'b'</span><span class="token punctuation">,</span> <span class="token string">'c'</span><span class="token punctuation">]</span><span class="token punctuation">;</span>

letters<span class="token punctuation">.</span><span class="token function">concat</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">,</span> <span class="token punctuation">[</span><span class="token number">2</span><span class="token punctuation">,</span> <span class="token number">3</span><span class="token punctuation">]</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// ['a', 'b', 'c', 1, 2, 3]</span>
</code></pre></div></li> <li><p>concatenating nested arrays</p> <div class="language-js extra-class"><pre class="language-js"><code><span class="token keyword">const</span> num1 <span class="token operator">=</span> <span class="token punctuation">[</span><span class="token punctuation">[</span><span class="token number">1</span><span class="token punctuation">]</span><span class="token punctuation">]</span><span class="token punctuation">;</span>
<span class="token keyword">const</span> num2 <span class="token operator">=</span> <span class="token punctuation">[</span><span class="token number">2</span><span class="token punctuation">,</span> <span class="token punctuation">[</span><span class="token number">3</span><span class="token punctuation">]</span><span class="token punctuation">]</span><span class="token punctuation">;</span>

num1<span class="token punctuation">.</span><span class="token function">concat</span><span class="token punctuation">(</span>num2<span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// [[1], 2, [3]]</span>
num1<span class="token punctuation">[</span><span class="token number">0</span><span class="token punctuation">]</span><span class="token punctuation">.</span><span class="token function">push</span><span class="token punctuation">(</span><span class="token number">4</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// [[1, 4], 2, [3]]</span>
</code></pre></div></li></ul> <h2 id="array-prototype-includes"><a href="#array-prototype-includes" class="header-anchor">#</a> Array.prototype.includes</h2> <h3 id="_1-语法-2"><a href="#_1-语法-2" class="header-anchor">#</a> 1. 语法</h3> <div class="custom-block danger"><p class="custom-block-title">WARNING</p> <p>arr.includes(valueToFind[, fromIndex])</p></div> <p>参数：</p> <ul><li>valueToFind：需要查找的元素；</li> <li>fromIndex：从 fromIndex 索引处开始查找 valueToFind，可为负值。</li></ul> <p>返回值：</p> <p>一个布尔值。</p> <h3 id="_2-描述-2"><a href="#_2-描述-2" class="header-anchor">#</a> 2. 描述</h3> <p>includes 方法用来判断一个数组是否包含一个指定的值，包含返回 true，否则返回 false。</p> <blockquote><p>个人在日常开发中常用场景：</p> <ul><li>常用于替代多个连续的 &amp;&amp; 操作。</li></ul></blockquote> <h3 id="_3-示例-2"><a href="#_3-示例-2" class="header-anchor">#</a> 3. 示例</h3> <ul><li><p>fromIndex is greater than or equal to the array length</p> <div class="language-js extra-class"><pre class="language-js"><code><span class="token keyword">const</span> arr <span class="token operator">=</span> <span class="token punctuation">[</span><span class="token string">'a'</span><span class="token punctuation">,</span> <span class="token string">'b'</span><span class="token punctuation">,</span> <span class="token string">'c'</span><span class="token punctuation">]</span><span class="token punctuation">;</span>

arr<span class="token punctuation">.</span><span class="token function">includes</span><span class="token punctuation">(</span><span class="token string">'c'</span><span class="token punctuation">,</span> <span class="token number">3</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// false</span>
arr<span class="token punctuation">.</span><span class="token function">inclueds</span><span class="token punctuation">(</span><span class="token string">'c'</span><span class="token punctuation">,</span> <span class="token number">100</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// false</span>
</code></pre></div></li> <li><p>computed index is less than o</p> <div class="language-js extra-class"><pre class="language-js"><code><span class="token keyword">const</span> arr <span class="token operator">=</span> <span class="token punctuation">[</span><span class="token string">'a'</span><span class="token punctuation">,</span> <span class="token string">'b'</span><span class="token punctuation">,</span> <span class="token string">'c'</span><span class="token punctuation">]</span><span class="token punctuation">;</span>

arr<span class="token punctuation">.</span><span class="token function">includes</span><span class="token punctuation">(</span><span class="token string">'a'</span><span class="token punctuation">,</span> <span class="token operator">-</span><span class="token number">100</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// true</span>
arr<span class="token punctuation">.</span><span class="token function">includes</span><span class="token punctuation">(</span><span class="token string">'b'</span><span class="token punctuation">,</span> <span class="token operator">-</span><span class="token number">100</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// true</span>
arr<span class="token punctuation">.</span><span class="token function">includes</span><span class="token punctuation">(</span><span class="token string">'c'</span><span class="token punctuation">,</span> <span class="token operator">-</span><span class="token number">100</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// true</span>
arr<span class="token punctuation">.</span><span class="token function">includes</span><span class="token punctuation">(</span><span class="token string">'a'</span><span class="token punctuation">,</span> <span class="token operator">-</span><span class="token number">2</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// false // 3 + (-2) = 1</span>
</code></pre></div></li> <li><p>includes() used as a generic method</p> <div class="language-js extra-class"><pre class="language-js"><code><span class="token punctuation">(</span><span class="token keyword">function</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
  console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token punctuation">[</span><span class="token punctuation">]</span><span class="token punctuation">.</span><span class="token function">includes</span><span class="token punctuation">.</span><span class="token function">call</span><span class="token punctuation">(</span>arguments<span class="token punctuation">,</span> <span class="token string">'a'</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// true</span>
  console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token punctuation">[</span><span class="token punctuation">]</span><span class="token punctuation">.</span><span class="token function">includes</span><span class="token punctuation">.</span><span class="token function">call</span><span class="token punctuation">(</span>arguments<span class="token punctuation">,</span> <span class="token string">'d'</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// false</span>
<span class="token punctuation">}</span><span class="token punctuation">)</span><span class="token punctuation">(</span><span class="token string">'a'</span><span class="token punctuation">,</span><span class="token string">'b'</span><span class="token punctuation">,</span><span class="token string">'c'</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
</code></pre></div></li></ul> <h2 id="array-prototype-indexof"><a href="#array-prototype-indexof" class="header-anchor">#</a> Array.prototype.indexOf</h2> <h3 id="_1-语法-3"><a href="#_1-语法-3" class="header-anchor">#</a> 1. 语法</h3> <div class="custom-block danger"><p class="custom-block-title">WARNING</p> <p>arr.indexOf(searchElement[, fromIndex = 0])</p></div> <p>参数：</p> <ul><li>searchElement：要查找的元素；</li> <li>fromIndex：开始查找的位置。</li></ul> <p>返回值：</p> <p>首个被找到的元素在数组中的索引位置，若没有找到则返回 -1。</p> <h3 id="_2-描述-3"><a href="#_2-描述-3" class="header-anchor">#</a> 2. 描述</h3> <p>描述即返回值。</p> <blockquote><p>个人在日常开发中常用场景：</p> <ul><li>查找索引，判断元素是否存在。</li></ul></blockquote> <h3 id="_3-示例-3"><a href="#_3-示例-3" class="header-anchor">#</a> 3. 示例</h3> <ul><li><p>finding all the occurrences of an element</p> <div class="language-js extra-class"><pre class="language-js"><code><span class="token keyword">let</span> indices <span class="token operator">=</span> <span class="token punctuation">[</span><span class="token punctuation">]</span><span class="token punctuation">;</span>
<span class="token keyword">const</span> array <span class="token operator">=</span> <span class="token punctuation">[</span><span class="token string">'a'</span><span class="token punctuation">,</span> <span class="token string">'b'</span><span class="token punctuation">,</span> <span class="token string">'a'</span><span class="token punctuation">,</span> <span class="token string">'c'</span><span class="token punctuation">,</span> <span class="token string">'a'</span><span class="token punctuation">,</span> <span class="token string">'d'</span><span class="token punctuation">]</span><span class="token punctuation">;</span>
<span class="token keyword">const</span> element <span class="token operator">=</span> <span class="token string">'a'</span><span class="token punctuation">;</span>
<span class="token keyword">let</span> idx <span class="token operator">=</span> array<span class="token punctuation">.</span><span class="token function">indexOf</span><span class="token punctuation">(</span>element<span class="token punctuation">)</span><span class="token punctuation">;</span>

<span class="token keyword">while</span> <span class="token punctuation">(</span>idx <span class="token operator">!==</span> <span class="token operator">-</span><span class="token number">1</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
  indices<span class="token punctuation">.</span><span class="token function">push</span><span class="token punctuation">(</span>idx<span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// [0, 2, 4]</span>
  idx <span class="token operator">=</span> array<span class="token punctuation">.</span><span class="token function">indexOf</span><span class="token punctuation">(</span>element<span class="token punctuation">,</span> idx <span class="token operator">+</span> <span class="token number">1</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
</code></pre></div></li> <li><p>finding if an element exists in the array or not and updating the array</p> <div class="language-js extra-class"><pre class="language-js"><code><span class="token keyword">function</span> <span class="token function">updateVegetablesCollection</span><span class="token punctuation">(</span><span class="token parameter">veggies<span class="token punctuation">,</span> veggie</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
  <span class="token keyword">if</span> <span class="token punctuation">(</span>veggies<span class="token punctuation">.</span><span class="token function">indexOf</span><span class="token punctuation">(</span>veggie<span class="token punctuation">)</span> <span class="token operator">===</span> <span class="token operator">-</span><span class="token number">1</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    veggies<span class="token punctuation">.</span><span class="token function">push</span><span class="token punctuation">(</span>veggie<span class="token punctuation">)</span><span class="token punctuation">;</span>
    console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token string">'New veggies collection is : '</span> <span class="token operator">+</span> veggies<span class="token punctuation">)</span><span class="token punctuation">;</span>
  <span class="token punctuation">}</span> <span class="token keyword">else</span> <span class="token keyword">if</span> <span class="token punctuation">(</span>veggies<span class="token punctuation">.</span><span class="token function">indexOf</span><span class="token punctuation">(</span>veggie<span class="token punctuation">)</span> <span class="token operator">&gt;</span> <span class="token operator">-</span><span class="token number">1</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
		console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span>veggie <span class="token operator">+</span> <span class="token string">' already exists in the veggies collection.'</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
	<span class="token punctuation">}</span>
<span class="token punctuation">}</span>

<span class="token keyword">let</span> veggies <span class="token operator">=</span> <span class="token punctuation">[</span><span class="token string">'potato'</span><span class="token punctuation">,</span> <span class="token string">'tomato'</span><span class="token punctuation">,</span> <span class="token string">'chillies'</span><span class="token punctuation">,</span> <span class="token string">'green-pepper'</span><span class="token punctuation">]</span><span class="token punctuation">;</span>
<span class="token function">updateVegetablesCollection</span><span class="token punctuation">(</span>veggies<span class="token punctuation">,</span> <span class="token string">'spinach'</span><span class="token punctuation">)</span><span class="token punctuation">;</span> 
<span class="token comment">// New veggies collection is : potato,tomato,chillies,green-pepper,spinach</span>
<span class="token function">updateVegetablesCollection</span><span class="token punctuation">(</span>veggies<span class="token punctuation">,</span> <span class="token string">'spinach'</span><span class="token punctuation">)</span><span class="token punctuation">;</span> 
<span class="token comment">// spinach already exists in the veggies collection.</span>
</code></pre></div></li></ul> <h2 id="array-prototype-join"><a href="#array-prototype-join" class="header-anchor">#</a> Array.prototype.join</h2> <h3 id="_1-语法-4"><a href="#_1-语法-4" class="header-anchor">#</a> 1. 语法</h3> <div class="custom-block danger"><p class="custom-block-title">WARNING</p> <p>arr.join([separator])</p></div> <p>参数：</p> <ul><li>separator：指定一个字符串来分隔数组的每个元素，默认为 <code>,</code>。</li></ul> <p>返回值：</p> <p>一个所有数组元素连接的字符串，如果 <code>arr.length</code> 为0，则返回空字符串。</p> <h3 id="_2-描述-4"><a href="#_2-描述-4" class="header-anchor">#</a> 2. 描述</h3> <p>描述即返回值。</p> <blockquote><p>个人在日常开发中常用场景：</p> <ul><li>字符串拆分重组。</li></ul></blockquote> <h3 id="_3-示例-4"><a href="#_3-示例-4" class="header-anchor">#</a> 3. 示例</h3> <ul><li><p>joining an array four different ways</p> <div class="language-js extra-class"><pre class="language-js"><code><span class="token keyword">const</span> a <span class="token operator">=</span> <span class="token punctuation">[</span><span class="token string">'Wind'</span><span class="token punctuation">,</span> <span class="token string">'Water'</span><span class="token punctuation">,</span> <span class="token string">'Fire'</span><span class="token punctuation">]</span><span class="token punctuation">;</span>
a<span class="token punctuation">.</span><span class="token function">join</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 'Wind,Water,Fire'</span>
a<span class="token punctuation">.</span><span class="token function">join</span><span class="token punctuation">(</span><span class="token string">', '</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 'Wind, Water, Fire'</span>
a<span class="token punctuation">.</span><span class="token function">join</span><span class="token punctuation">(</span><span class="token string">' + '</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 'Wind + Water + Fire'</span>
a<span class="token punctuation">.</span><span class="token function">join</span><span class="token punctuation">(</span><span class="token string">''</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 'WindWaterFire'</span>
</code></pre></div></li> <li><p>joining an array-like object</p> <div class="language-js extra-class"><pre class="language-js"><code><span class="token keyword">function</span> <span class="token function">f</span><span class="token punctuation">(</span><span class="token parameter">a<span class="token punctuation">,</span> b<span class="token punctuation">,</span> c</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
  <span class="token keyword">return</span> <span class="token class-name">Array</span><span class="token punctuation">.</span>prototype<span class="token punctuation">.</span><span class="token function">join</span><span class="token punctuation">.</span><span class="token function">call</span><span class="token punctuation">(</span>arguments<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token function">f</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">,</span> <span class="token string">'a'</span><span class="token punctuation">,</span> <span class="token boolean">true</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// '1,a,true'</span>
</code></pre></div></li></ul> <h2 id="array-prototype-lastindexof"><a href="#array-prototype-lastindexof" class="header-anchor">#</a> Array.prototype.lastIndexOf</h2> <p>indexOf 的反向行为，不做描述。</p> <h2 id="array-prototype-slice"><a href="#array-prototype-slice" class="header-anchor">#</a> Array.prototype.slice</h2> <h3 id="_1-语法-5"><a href="#_1-语法-5" class="header-anchor">#</a> 1. 语法</h3> <div class="custom-block danger"><p class="custom-block-title">WARNING</p> <p>arr.slice([begin[, end]])</p></div> <p>参数：</p> <ul><li>begin：提取起始处的索引，默认为 0；</li> <li>end：提取终止处的索引，默认为 length-1。</li></ul> <p>返回值：</p> <p>一个含有被提取元素的新数组。</p> <h3 id="_2-描述-5"><a href="#_2-描述-5" class="header-anchor">#</a> 2. 描述</h3> <p>slice 不会修改原数组，只会返回一个浅拷贝的新数组。</p> <blockquote><p>个人在日常开发中常用场景：</p> <ul><li>截取内容。</li></ul></blockquote> <h3 id="_3-示例-5"><a href="#_3-示例-5" class="header-anchor">#</a> 3. 示例</h3> <div class="language-js extra-class"><pre class="language-js"><code><span class="token keyword">const</span> fruits <span class="token operator">=</span> <span class="token punctuation">[</span><span class="token string">'Banana'</span><span class="token punctuation">,</span> <span class="token string">'Orange'</span><span class="token punctuation">,</span> <span class="token string">'Lemon'</span><span class="token punctuation">,</span> <span class="token string">'Apple'</span><span class="token punctuation">,</span> <span class="token string">'Mango'</span><span class="token punctuation">]</span><span class="token punctuation">;</span>
fruits<span class="token punctuation">.</span><span class="token function">slice</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">,</span> <span class="token number">3</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// ['Orange','Lemon']</span>
</code></pre></div><h2 id="array-prototype-tostring"><a href="#array-prototype-tostring" class="header-anchor">#</a> Array.prototype.toString</h2> <h3 id="_1-语法-6"><a href="#_1-语法-6" class="header-anchor">#</a> 1. 语法</h3> <div class="custom-block danger"><p class="custom-block-title">WARNING</p> <p>arr.toString()</p></div> <p>返回值：</p> <p>一个表示指定的数组及元素的字符串。</p> <h3 id="_2-描述-6"><a href="#_2-描述-6" class="header-anchor">#</a> 2. 描述</h3> <p>Array 对象覆盖了 Object 的 toString 方法，当一个数组被作为文本值或者进行字符串连接操作时，将会自动调用其 toString 方法。</p> <blockquote><p>个人在日常开发中常用场景：</p> <ul><li>常用于数组转为字符串。</li></ul></blockquote> <h3 id="_3-示例-6"><a href="#_3-示例-6" class="header-anchor">#</a> 3. 示例</h3> <div class="language-js extra-class"><pre class="language-js"><code><span class="token keyword">const</span> array <span class="token operator">=</span> <span class="token punctuation">[</span><span class="token number">1</span><span class="token punctuation">,</span> <span class="token number">2</span><span class="token punctuation">,</span> <span class="token string">'a'</span><span class="token punctuation">,</span> <span class="token string">'1a'</span><span class="token punctuation">]</span><span class="token punctuation">;</span>
arrar<span class="token punctuation">.</span><span class="token function">toString</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// &quot;1,2,a,1a&quot;</span>
</code></pre></div><h2 id="array-prototype-tolocalestring"><a href="#array-prototype-tolocalestring" class="header-anchor">#</a> Array.prototype.toLocaleString</h2> <h3 id="_1-语法-7"><a href="#_1-语法-7" class="header-anchor">#</a> 1. 语法</h3> <div class="custom-block danger"><p class="custom-block-title">WARNING</p> <p>arr.toLocaleString([locales[,options]])</p></div> <p>参数：</p> <ul><li>locales：带有 BCP 47 语言标记的字符串或字符串数组；</li> <li>options：一个可配置属性的对象。</li></ul> <p>返回值：</p> <p>表示数组元素的字符串。</p> <h3 id="_2-描述-7"><a href="#_2-描述-7" class="header-anchor">#</a> 2. 描述</h3> <p>toLocaleString 返回一个字符串表示数组中的元素。数组中的元素将使用各自的 toLocaleString 方法转为字符串，这些字符串将使用一个特定语言环境的字符串隔开。</p> <blockquote><p>个人在日常开发中常用场景：</p> <ul><li>早期使用过该方法将时间转换为本地时间，后来使用 dayjs，moment 等时间库替代了。</li></ul></blockquote> <h3 id="_3-示例-7"><a href="#_3-示例-7" class="header-anchor">#</a> 3. 示例</h3> <div class="language-js extra-class"><pre class="language-js"><code><span class="token comment">// Object：Object.prototype.toLocaleString()</span>
<span class="token comment">// Number：Number.prototype.toLocaleString()</span>
<span class="token comment">// Date：Date.prototype.toLocaleString()</span>

<span class="token keyword">let</span> prices <span class="token operator">=</span> <span class="token punctuation">[</span><span class="token string">'￥7'</span><span class="token punctuation">,</span> <span class="token number">500</span><span class="token punctuation">,</span> <span class="token number">8123</span><span class="token punctuation">,</span> <span class="token number">12</span><span class="token punctuation">]</span><span class="token punctuation">;</span> 
prices<span class="token punctuation">.</span><span class="token function">toLocaleString</span><span class="token punctuation">(</span><span class="token string">'ja-JP'</span><span class="token punctuation">,</span> <span class="token punctuation">{</span> style<span class="token operator">:</span> <span class="token string">'currency'</span><span class="token punctuation">,</span> currency<span class="token operator">:</span> <span class="token string">'JPY'</span> <span class="token punctuation">}</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// &quot;￥7,￥500,￥8,123,￥12&quot;</span>
</code></pre></div></div> <footer class="page-edit"><!----> <div class="last-updated"><span class="prefix">上次更新:</span> <span class="time">2020年3月17日星期二下午2点47分</span></div></footer> <div class="page-nav"><p class="inner"><span class="prev">
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